Engaging and disengaging device, seat belt retractor, and seat belt assembly

ABSTRACT

An engagement and disengagement device used in a seat belt retractor includes a first rotating member and a second rotating member configured to be coaxial, and a transmission member disposed between the first and second rotating members. The first rotating member defines an engagement portion on a radial inner surface thereof, and the distance from the engagement portion to an axis of rotation gradually increases in a first direction of rotation. The transmission member can rotate between an engagement position and a non-engagement position relative to the first rotating member.

TECHNICAL FIELD

The present invention relates to a seat belt retractor used in avehicle. More specifically, the present invention relates to anengagement and disengagement device used in a seat belt retractor. Incases such as an emergency deceleration of a vehicle, the engagement anddisengagement device rotates a seat belt reel in a winding direction bymeans of a driving unit, and can reversibly allow the seat belt reel todisengage from a driving device.

BACKGROUND

Existing seat belt retractors can provide functions such aspre-collision protection, man-machine interaction during driving, andcomfort. Before a control unit determines that a vehicle may crash, anactive seat belt retractor can retract a certain length of a seat beltby means of a motor so as to slightly bind a passenger; when the controlunit determines that the risk of crashing disappears, the active seatbelt retractor allows the seat belt to be freely pulled.

The motor of the seat belt retractor has small output torque. Therefore,clutches for seat belt retractors are mainly toothed clutches. Suchclutches have a long engagement and disengagement delay, a great impact,and loud noise, and inner and outer teeth thereof are not synchronized.

Existing overrunning clutches employing balls are mainly classified intotwo categories: clutches having no cages and clutches having cages. In aclutch having no cage, balls are fixed in an inner ring or an outerring, and an input end and an output end cannot completely disengagefrom each other. When the clutch is used in a seat belt, if the motoracts as an input end, motion control can be performed. However, becauseof incomplete disengagement, the seat belt is jammed if a passengerpulls or retracts the seat belt. In a clutch having a cage, inertia ismainly provided by the cage, engagement is performed when an input endis activated at a high speed, and the input end and an output end cancompletely disengage from each other. However, because inertia isrequired when performing engagement and disengagement, the input endneeds to be activated at a high speed. When the clutch is used in a seatbelt, the functions of comfort and man-machine interaction, whichrequire low-speed activation, cannot be achieved.

Therefore, an improved engagement and disengagement device used in aseat belt retractor is needed.

SUMMARY

An objective of the present invention is to provide an engagement anddisengagement device capable of engaging and disengaging at a lowrotational speed, a seat belt retractor, and a seat belt assembly. Anaspect of the present invention provides an engagement and disengagementdevice in which an input end and an output end are completely separatedfrom each other after disengagement is performed, a seat belt retractor,and a seat belt assembly. Another aspect of the present inventionprovides an engagement and disengagement device in which a small impactis generated when performing engagement or disengagement, a seat beltretractor, and a seat belt assembly.

An aspect of the present invention provides an engagement anddisengagement device used in a seat belt retractor, comprising: a firstrotating member that can be driven to rotate around an axis of rotation;a second rotating member, wherein the second rotating member and thefirst rotating member are configured to be coaxial, and the secondrotating member is used to be connected to a reel of the seat beltretractor in an anti-torsion manner; and a transmission member disposedbetween the first rotating member and the second rotating member,wherein the first rotating member can transmit, in a first direction ofrotation, torque to the second rotating member via the transmissionmember, wherein the first rotating member defines an engagement portionon a radial inner surface thereof, the distance from the engagementportion to the axis of rotation gradually increases in the firstdirection of rotation, and the engagement portion is used to engage withthe transmission member; and wherein the transmission member can rotatebetween an engagement position and a non-engagement position relative tothe first rotating member, wherein when the transmission member is atthe engagement position, the transmission member engages with both thefirst rotating member and the second rotating member, such that thefirst rotating member, the second rotating member, and the transmissionmember can rotate together; when the transmission member is at thenon-engagement position, the transmission member does not engage withthe first rotating member and the second rotating member, such that thefirst rotating member and the second rotating member can freely rotaterelative to each other.

According to an embodiment of the present invention, the transmissionmember comprises a cage and a transmission element, and the transmissionelement is disposed in the cage, and can move radially in a spacedefined between the engagement portion of the first rotating member anda radial outer surface of the second rotating member.

According to an embodiment of the present invention, when thetransmission member is at the engagement position, no radial gap existsboth between the transmission element and the engagement portion of thefirst rotating member, and between the transmission element and theradial outer surface of the second rotating member.

According to an embodiment of the present invention, the transmissionelement is a rolling element.

According to an embodiment of the present invention, the cage has a ringshape, and is rotatably sleeved on the second rotating member.

According to an embodiment of the present invention, the cage defines aretaining portion; the transmission element is disposed in the retainingportion; the retaining portion restricts axial movement of thetransmission element relative to the cage.

According to an embodiment of the present invention, the cage comprisesa first position-limiting portion located on a radial outer surfacethereof; the first rotating member comprises a second position-limitingportion located on the radial inner surface thereof; and the firstposition-limiting portion and the second position-limiting portion canwork with each other to restrict an angle of rotation of the cagerelative to the first rotating member.

According to an embodiment of the present invention, the firstposition-limiting portion is located on an axial side of the cage, andthe second position-limiting portion is located on a corresponding axialside of the first rotating member, wherein the second position-limitingportion and the engagement portion are sequentially axially disposed,and the first position-limiting portion is axially located on an outerside of the engagement portion.

According to an embodiment of the present invention, the engagement anddisengagement device further comprises a first elastic componentconnected to the cage so as to elastically retain the transmissionelement in a radial direction.

According to an embodiment of the present invention, the first elasticcomponent is a torsion spring.

According to an embodiment of the present invention, the cage comprisestwo side rings and a plurality of connecting pieces, the plurality ofconnecting pieces being spaced apart in a circumferential direction,wherein the side rings and the connecting pieces define the retainingportion, and an end portion of the first elastic component is connectedto the connecting pieces.

According to an embodiment of the present invention, the engagement anddisengagement device further comprises a housing, wherein the housingdefines an accommodation cavity to accommodate the first rotating memberand the transmission member.

According to an embodiment of the present invention, the first rotatingmember is rotatably supported in the housing.

According to an embodiment of the present invention, the first rotatingmember comprises an annular recess extending axially; the housingcomprises an annular protrusion extending axially; and the annularprotrusion can be inserted into the annular recess so as to rotatablysupport the first rotating member.

According to an embodiment of the present invention, the engagement anddisengagement device further comprises a cover plate connected to thehousing so as to seal the accommodation cavity.

According to an embodiment of the present invention, the engagement anddisengagement device further comprises a second elastic componentdisposed on an axial side of the transmission member away from the coverplate so as to apply a biasing force causing the transmission member toabut the cover plate.

According to an embodiment of the present invention, the second elasticcomponent is a wave spring.

Another aspect of the present invention provides a seat belt retractor,comprising: the engagement and disengagement device according to theembodiment of the present invention; a driving device used to drive thefirst rotating member of the engagement and disengagement device torotate around the axis of rotation; and a reel connected to the secondrotating member of the engagement and disengagement device in ananti-torsion manner, wherein the reel can wind a seat belt when rotatingin the first direction of rotation, and can unwind the seat belt whenrotating in the second direction of rotation opposite to the firstdirection of rotation.

Another aspect of the present invention provides a seat belt assembly,comprising: a seat belt retractor, comprising: the engagement anddisengagement device according to the embodiment of the presentinvention; a driving device used to drive the first rotating member ofthe engagement and disengagement device to rotate around the axis ofrotation; and a reel connected to the second rotating member of theengagement and disengagement device in an anti-torsion manner; and aseat belt having one end portion fixed to the reel, wherein the reel canwind the seat belt when rotating in the first direction of rotation, andcan unwind the seat belt when rotating in the second direction ofrotation opposite to the first direction of rotation.

According to an embodiment of the present invention, when the engagementand disengagement device is in a disengaged state, the transmissionelement and the second rotating member are radially spaced apart fromeach other, such that an input end and an output end of the engagementand disengagement device can be completely separated from each other. Inan initial stage of switching a state of the engagement anddisengagement device, due to a frictional force between the cage and thecover plate, the transmission element can cause the first rotatingmember and the second rotating member to engage with each other at asmaller angle of rotation. Therefore, the engagement and disengagementdevice of the present invention can reduce an engagement anddisengagement delay, so as to wind a seat belt more quickly to provide apassenger with protection. In addition, due to the frictional forcebetween the cage and the cover plate, the engagement and disengagementdevice can also perform engagement and disengagement even at a lowrotational speed of a motor, thereby reducing noise and an impact.

These and other aspects and advantages of the present invention will beclearer after the following detailed description of the presentinvention is read with reference to the accompanying drawings.

It should be understood that the foregoing introduction and thefollowing detailed description are merely exemplary and illustrative,and are not intended to limit the invention to be protected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of an engagement and disengagement deviceused in a seat belt retractor according to an embodiment of the presentinvention;

FIG. 2 is a side view of the engagement and disengagement deviceaccording to an embodiment of the present invention;

FIG. 3 is a cross-sectional view of the engagement and disengagementdevice according to an embodiment of the present invention;

FIG. 4 is a side view of the engagement and disengagement deviceaccording to an embodiment of the present invention; and

FIG. 5 is a cross-sectional view of the engagement and disengagementdevice according to an embodiment of the present invention.

DETAILED DESCRIPTION

The embodiments of the present invention will be described below withreference to the drawings. The detailed description and drawings beloware used exemplarily to illustrate the principles of the presentinvention. The present invention is not limited to the describedpreferred embodiments. The scope of the present invention is defined bythe claims. The present invention is described in detail herein withreference to exemplary embodiments, and some embodiments are illustratedin the accompanying drawings. The following description is provided withreference to the accompanying drawings. Unless otherwise indicated, thesame reference numerals in different accompanying drawings represent thesame or similar elements. The solutions described in the followingexemplary embodiments do not represent all of the solutions of thepresent invention. Instead, these solutions are merely examples ofsystems and methods according to aspects of the present inventioninvolved in the appended claims.

FIG. 1 is an exploded view of an engagement and disengagement deviceused in a seat belt retractor according to an embodiment of the presentinvention. As shown in FIG. 1 , the engagement and disengagement devicecan include a first rotating member 10, a second rotating member 20, anda transmission member 30.

The first rotating member 10 can be driven to rotate around an axis ofrotation thereof. The first rotating member 10 can have a hollowstructure, such that at least part of the second rotating member 20passes therethrough. In some embodiments, the first rotating member 10includes a toothed portion 11 located on an outer peripheral surfacethereof. The toothed portion 11 can engage with a driving device of theseat belt retractor by means of a gear mechanism, such as by means of aworm gear and worm, a rack and pinion, or the like.

According to an embodiment of the present invention, the first rotatingmember 10 includes an engagement portion 12 defined on a radial innersurface thereof. In an exemplary embodiment, the first rotating member10 defines a plurality of, for example four, engagement portions 12 onthe radial inner surface thereof. The engagement portion 12 is used toengage with the transmission member 30.

The second rotating member 20 and the first rotating member 10 areconfigured to be coaxial. The second rotating member 20 can be connectedto a reel of the seat belt retractor in an anti-torsion manner, so as totransmit torque to the reel. In an exemplary embodiment, at least partof a radial outer surface of the second rotating member 20 can engagewith the transmission member 30.

The transmission member 30 is disposed between the first rotating member10 and the second rotating member 20. In an exemplary embodiment, thetransmission member 30 can include a cage 31 and a transmission element32. The cage 31 is used to retain one or a plurality of transmissionelements 32. In some embodiments, the number of transmission elements 32is equal to the number of engagement portions 12. In some embodiments,the transmission element 32 can be a rolling element, such as acylindrical roller, a needle roller, or the like.

In an exemplary embodiment, the cage 31 is annular, and can be rotatablysleeved on the second rotating member 20. In the exemplary embodimentshown in FIG. 1 , the cage 31 can include two side rings 311 and 312 anda plurality of connecting pieces 313, the plurality of connecting piecesbeing spaced apart in a circumferential direction. The connecting pieces313 are connected to the side rings 311 and 312. In some embodiments,the connecting pieces 313 can have identical intervals in thecircumferential direction. The connecting pieces 313 and the side rings311 and 312 define a plurality of retaining portions. The transmissionelement 32 can be disposed and retained in the retaining portion. Theretaining portion of the cage 31 can restrict axial movement of thetransmission element 32 relative to the cage 31, for example, by meansof the two side rings 311 and 312.

According to an embodiment of the present invention, the radial distancefrom the engagement portion 12 of the first rotating member 10 to theaxis of rotation gradually increases in a first direction of rotation(see description below). The transmission element 32 can move radiallyin a space defined between the engagement portion 12 of the firstrotating member 10 and the radial outer surface of the second rotatingmember 20.

FIG. 2 is a side view of the engagement and disengagement deviceaccording to an embodiment of the present invention. FIG. 3 is across-sectional view of the engagement and disengagement deviceaccording to an embodiment of the present invention. As shown in FIG. 2and FIG. 3 , the distance from the engagement portion 12 to the axis ofrotation gradually increases in a first direction of rotation A (thecounterclockwise direction). Viewed axially, the engagement portion 12can have a shape of any appropriate curve, for example, an evolvent.FIG. 2 and FIG. 3 show that the engagement and disengagement device isin an engaged state, where the transmission element 32 of thetransmission member 30 radially maintains in gapless engagement withboth the first rotating member 10 (the engagement portion 12) and theradial outer surface of the second rotating member 20.

FIG. 4 is a side view of the engagement and disengagement deviceaccording to an embodiment of the present invention. FIG. 5 is across-sectional view of the engagement and disengagement deviceaccording to an embodiment of the present invention. As shown in FIG. 4and FIG. 5 , the engagement and disengagement device is in a disengagedstate, where the transmission element 32 of the transmission member 30does not engage with the second rotating member 20.

The transmission member 30 can rotate between an engagement position anda non-engagement position relative to the first rotating member 10.

In the engaged state shown in FIG. 2 and FIG. 3 , the transmissionelement 32 radially engages with both the first rotating member 10 (theengagement portion 12) and the second rotating member 20. When the firstrotating member 10 rotates in the first direction of rotation A, thefirst rotating member 10 can transmit torque to the second rotatingmember 20 via the transmission member 30 (for example, the transmissionelement 32), such that the first rotating member 10, the transmissionelement 32, and the second rotating member 20 can rotate together.

In the engaged state of the engagement and disengagement device, whenthe first rotating member 10 rotates in a second direction of rotation Bopposite to the first direction of rotation A, the transmission element32 of the transmission member 30 can disengage from the second rotatingmember 20 (as shown in FIG. 4 and FIG. 5 ), such that the first rotatingmember 10 and the second rotating member 20 can freely rotate relativeto each other.

According to some embodiments of the present invention, the transmissionmember 30 can further include an elastic component 33, so as toelastically retain the transmission element 32 in a radial direction. Insome embodiments, the elastic component 33 can be a torsion spring. Inan exemplary embodiment, the elastic component 33 can be connected tothe cage 31. For example, an end portion of the elastic component 33 canbe connected to the connecting piece 313 of the cage 31. In an exemplaryembodiment, the elastic component 33 can outwardly apply a biasingforce, in the radial direction, to the transmission element 32. Theelastic component 33 can have any appropriate shape or size, as long asthe elastic component 33 can radially support and reset the transmissionelement 32.

As shown in FIG. 3 , in the engaged state, the transmission element 32is subject to a force from the engagement portion 12, and thus overcomesthe biasing force from the elastic component 33. Thus, the transmissionelement 32 moves inwardly, in a radial direction, to engage with thesecond rotating member 20. As shown in FIG. 5 , in the disengaged state,the transmission element 32 is subject to the biasing force from theelastic component 33, and is spaced apart, in the radial direction, fromthe second rotating member 20.

According to an embodiment of the present invention, the engagement anddisengagement device can further include a housing 40 and a cover plate50, as shown in FIG. 1 . The housing 40 defines an accommodation cavity,so as to accommodate the first rotating member 10 and the transmissionmember 30. The cover plate 50 can be connected to the housing 40 so asto seal the accommodation cavity. In an exemplary embodiment, the coverplate 50 can be fixed to an axial end surface of the housing 40 by meansof, for example, a screw. The housing 40 and the cover plate 50 can eachhave a central through-hole, such that at least part of the secondrotating member 20 can pass therethrough.

The housing 40 can serve as an axial bearing for the first rotatingmember 10, such that the first rotating member 10 can be rotatablysupported in the housing 40. In some embodiments, the first rotatingmember 10 includes an annular recess (not shown) extending axially, andthe housing 40 includes an annular protrusion 41 extending axially. Theannular protrusion 41 of the housing 40 can be inserted into the annularrecess of the first rotating member 10 so as to rotatably support thefirst rotating member 10.

According to some embodiments of the present invention, the cage 31 canfurther include a position-limiting portion 314 located on a radialouter surface thereof, and the first rotating member 10 can include aposition-limiting portion 13 located on the radial inner surfacethereof. The position-limiting portion 314 of the cage 31 and theposition-limiting portion 13 of the first rotating member 10 can workwith each other to restrict an angle of rotation of the cage 31 relativeto the first rotating member 10. In an exemplary embodiment, theposition-limiting portion 314 is located on an axial side (for example,the side close to the cover plate 50) of the cage 31, and theposition-limiting portion 13 is located on a corresponding axial side ofthe first rotating member 10. As shown in FIG. 4 , during operation ofthe engagement and disengagement device, when the position-limitingportion 314 and the position-limiting portion 13 abut each other, thefirst rotating member 10 and the cage 31 remain stationary relative toeach other.

In an exemplary embodiment, the engagement portion 12 and theposition-limiting portion 13 of the first rotating member 10 can besequentially axially arranged, as shown in FIG. 1 . In addition, theposition-limiting portion 314 of the cage 31 is axially disposed on anouter side of the engagement portion. In this case, engagement betweenthe first rotating member 10 and the transmission member 30 is notaffected by the position-limiting portions.

According to an embodiment of the present invention, the engagement anddisengagement device can further an elastic component 60. In anexemplary embodiment, the elastic component 60 is used to apply abiasing force causing the transmission member 30 to abut the cover plate50. In some embodiments, the elastic component 60 can be axiallydisposed between the cage 31 of the transmission member 30 and thehousing 40. In some embodiments, the elastic component 60 can be a wavespring. The elastic component 60 applies a biasing force to thetransmission member 30, such that a frictional force is generatedbetween the transmission member 30 and the cover plate 50. At the verybeginning of rotation of the first rotating member 10, the elasticcomponent 60 is subject to the frictional force and remains stationary,thereby facilitating rapid engagement or disengagement between thetransmission member 30 and the second rotating member 20.

A method for operating the engagement and disengagement device accordingto an embodiment of the present invention will be described below.

When the engagement and disengagement device is in the disengaged state,as shown in FIG. 4 and FIG. 5 , the transmission element 32 iscircumferentially located in a position on the engagement portion 12close to the toothed portion 11, and the transmission element 32 is, ina radial direction, outwardly subject to the biasing force from theelastic component 33, such that the transmission element 32 radiallydisengages from the second rotating member 20. When the disengaged stateis switched to the engaged state, the first rotating member 10 is firstdriven by the driving device to rotate in the first direction ofrotation A. Due to the biasing force from the elastic component 60, thetransmission member 30 is subject to the frictional force between thetransmission member 30 and the cover plate 50 so as to remain stationaryduring an initial stage. The engagement portion 12 of the first rotatingmember 10 is radially in gapless engagement with the transmissionelement 32 of the transmission member 30. As the first rotating member10 rotates, the engagement portion 12 applies a force to thetransmission element 32, such that the transmission element 32 radiallyand gradually approaches the radial outer surface of the second rotatingmember 20. When the transmission element 32 moves to be in gaplessengagement with the radial outer surface of the second rotating member20, the first rotating member 10 can drive, via the transmission element32, the second rotating member 20 to rotate, such that the engagementand disengagement device is in the engaged state, as shown in FIG. 2 andFIG. 3 .

When the engagement and disengagement device is in the disengaged state,as shown in FIG. 2 and FIG. 3 , the transmission element 32 iscircumferentially located in a position on the engagement portion 12away from the toothed portion 11. The transmission element 32 engageswith the engagement portion 12, and is radially inwardly subject to theforce from the engagement portion 12, so as to overcome the biasingforce from the elastic component 33 and radially engage with the secondrotating member 20. When the engaged state is switched to the disengagedstate, the first rotating member 10 is first driven by the drivingdevice to rotate in the second direction of rotation B. Due to thebiasing force from the elastic component 60, the transmission member 30is subject to the frictional force between the transmission member 30and the cover plate 50 so as to remain stationary during an initialstage. As the first rotating member 10 rotates, the elastic component 33outwardly applies a biasing force, in the radial direction, to thetransmission element 32, such that the transmission element 32 radiallyand gradually leaves the radial outer surface of the second rotatingmember 20. When the transmission element 32 moves to disengage from theradial outer surface of the second rotating member 20, the firstrotating member 10 and the second rotating member 20 can freely rotaterelative to each other, such that the engagement and disengagementdevice is in the disengaged state, as shown in FIG. 4 and FIG. 5 .

The transmission element in the above description is a rolling element.However, the present invention is not limited thereto. According to anembodiment of the present invention, the transmission element can alsobe in other forms, such as a wedge.

The transmission element in the above description is retained by thecage. However, the present invention is not limited thereto. Accordingto an embodiment of the present invention, the transmission element canalso be retained by the first rotating member or the second rotatingmember. For example, the elastic component 33 of the transmission member30 can be connected to the first rotating member 10 or the secondrotating member 20, such that the transmission element 32 is retainedvia a radial biasing force thereof.

The above describes that when the engagement and disengagement device isin the disengaged state, the transmission element 32 of the transmissionmember 30 does not engage with the second rotating member 20. However,the present invention is not limited thereto. According to an embodimentof the present invention, the engagement and disengagement device canalso be configured such that when the engagement and disengagementdevice is in the disengaged state, the transmission element 32 does notengage with the first rotating member 10 (for example, the engagementportion 12). For example, the elastic component 33 can inwardly apply abiasing force, in a radial direction, to the transmission element 32.When the first rotating member 10 rotates in the second direction ofrotation, the transmission element 32 radially and gradually leaves theengagement portion 12 of the first rotating member 10, such that theengagement and disengagement device is in the disengaged state.

The engagement and disengagement device according to the embodiment ofthe present invention can be applied to a seat belt retractor. The seatbelt retractor can include the aforementioned engagement anddisengagement device, a driving device, and a reel. The driving deviceis used to drive the first rotating member 10 of the engagement anddisengagement device to rotate around the axis of rotation. In anexemplary embodiment, the driving device can be a motor. For example,the motor can drive, via a gear mechanism (equivalent to a worm gear andworm, a rack and pinion, or the like), the first rotating member 10 torotate. The reel is connected to the second rotating member 20 of theengagement and disengagement device in an anti-torsion manner, and aseat belt can be wound around the reel. The reel can wind the seat beltwhen rotating in the first direction of rotation, and can unwind theseat belt when rotating in the second direction of rotation opposite tothe first direction of rotation. During operation, when the drivingdevice drives the first rotating member 10 to rotate in the firstdirection of rotation, the first rotating member 10 drives, via thetransmission member 30 of the engagement and disengagement device, thesecond rotating member 20 and the reel to rotate, so as wind a certainlength of the seat belt around the reel; when the driving device drivesthe first rotating member 10 to rotate in the second direction ofrotation, the first rotating member 10 and the second rotating member 20disengage from each other so as to be capable of freely rotatingrelative to each other, such that a passenger can freely pull the seatbelt.

The engagement and disengagement device according to the embodiment ofthe present invention can be applied to a seat belt assembly. The seatbelt assembly can include the aforementioned seat belt retractor and aseat belt, and one end portion of the seat belt is fixed to the reel ofthe seat belt retractor.

The mention of “one embodiment” or “an embodiment” in the descriptionindicates that the specific features, structures, or propertiesdescribed with reference to embodiments are included in at least oneembodiment. Therefore, the terms or variants thereof used in the wholedescription do not necessarily refer to the same embodiment.

Although the present invention has already been described with referenceto the exemplary embodiments, it shall be understood that the presentinvention is not limited to the constructions and methods described inthe above-mentioned embodiments. Contrarily, the present inventionintends to cover various modification examples and equivalentconfigurations. In addition, although various elements and method stepsof the disclosed invention are described in various exemplarycombinations and constructions, other combinations comprising more orfewer elements or methods also fall into the scope of the presentinvention.

The invention claimed is:
 1. An engagement and disengagement device usedin a seat belt retractor, comprising: a first rotating member which canbe driven to rotate around an axis of rotation; a second rotatingmember, wherein the second rotating member and the first rotating memberare configured to be coaxial, and the second rotating member is used tobe connected to a reel of the seat belt retractor; and a transmissionmember disposed between the first rotating member and the secondrotating member, wherein the first rotating member can transmit, in afirst direction of rotation, torque to the second rotating member viathe transmission member, wherein the first rotating member defines anengagement portion on a radial inner surface thereof, the distance fromthe engagement portion to the axis of rotation gradually increases inthe first direction of rotation, and the engagement portion is used toengage with the transmission member; and wherein the transmission membercan rotate between an engagement position and a non-engagement positionrelative to the first rotating member, wherein when the transmissionmember is at the engagement position, the transmission member engageswith both the first rotating member and the second rotating member, suchthat the first rotating member, the second rotating member, and thetransmission member can rotate together; when the transmission member isat the non-engagement position, the transmission member does not engagewith the first rotating member and the second rotating member, such thatthe first rotating member and the second rotating member can freelyrotate relative to each other.
 2. The engagement and disengagementdevice according to claim 1, wherein the transmission member comprises acage and a transmission element, and the transmission element isdisposed in the cage, and can move radially in a space defined betweenthe engagement portion of the first rotating member and a radial outersurface of the second rotating member.
 3. The engagement anddisengagement device according to claim 2, wherein when the transmissionmember is at the engagement position, no radial gap exists both betweenthe transmission element and the engagement portion of the firstrotating member, and between the transmission element and the radialouter surface of the second rotating member.
 4. The engagement anddisengagement device according to 3, wherein the transmission element isa rolling element.
 5. The engagement and disengagement device accordingto claim 2, wherein the cage has a ring shape, and is rotatably sleevedon the second rotating member.
 6. The engagement and disengagementdevice according to claim 5, wherein the cage defines a retainingportion; the transmission element is disposed in the retaining portion;the retaining portion restricts axial movement of the transmissionelement relative to the cage.
 7. The engagement and disengagement deviceaccording to claim 6, wherein the cage comprises a firstposition-limiting portion located on a radial outer surface thereof; thefirst rotating member comprises a second position-limiting portionlocated on the radial inner surface thereof; and the firstposition-limiting portion and the second position-limiting portion canwork with each other to restrict an angle of rotation of the cagerelative to the first rotating member.
 8. The engagement anddisengagement device according to claim 7, wherein the firstposition-limiting portion is located on an axial side of the cage, andthe second position-limiting portion is located on a corresponding axialside of the first rotating member, wherein the second position-limitingportion and the engagement portion are sequentially axially disposed,and the first position-limiting portion is axially located on an outerside of the engagement portion.
 9. The engagement and disengagementdevice according to claim 2, further comprising a first elasticcomponent connected to the cage so as to elastically retain thetransmission element in a radial direction.
 10. The engagement anddisengagement device according to claim 9, wherein the first elasticcomponent is a torsion spring.
 11. The engagement and disengagementdevice according to claim 9, wherein the cage comprises two side ringsand a plurality of connecting pieces, the plurality of connecting piecesbeing spaced apart in a circumferential direction, wherein the siderings and the connecting pieces define the retaining portion, and an endportion of the first elastic component is connected to the connectingpieces.
 12. The engagement and disengagement device according to claim1, further comprising a housing, wherein the housing defines anaccommodation cavity to accommodate the first rotating member and thetransmission member.
 13. The engagement and disengagement deviceaccording to claim 12, wherein the first rotating member is rotatablysupported in the housing.
 14. The engagement and disengagement deviceaccording to claim 12, wherein the first rotating member comprises anannular recess extending axially; the housing comprises an annularprotrusion extending axially; and the annular protrusion can be insertedinto the annular recess so as to rotatably support the first rotatingmember.
 15. The engagement and disengagement device according to claim12, further comprising a cover plate connected to the housing so as toseal the accommodation cavity.
 16. The engagement and disengagementdevice according to claim 15, further comprising a second elasticcomponent disposed on an axial side of the transmission member away fromthe cover plate so as to apply a biasing force causing the transmissionmember to abut the cover plate.
 17. The engagement and disengagementdevice according to claim 16, wherein the second elastic component is awave spring.
 18. A seat belt retractor, comprising: the engagement anddisengagement device according to claim 1; a driving device used todrive the first rotating member of the engagement and disengagementdevice to rotate around the axis of rotation; and a reel connected tothe second rotating member of the engagement and disengagement device,wherein the reel can wind a seat belt when rotating in the firstdirection of rotation, and can unwind the seat belt when rotating in thesecond direction of rotation opposite to the first direction ofrotation.
 19. A seat belt assembly, comprising: a seat belt retractor,comprising: the engagement and disengagement device according to claim1; a driving device used to drive the first rotating member of theengagement and disengagement device to rotate around the axis ofrotation; and a reel connected to the second rotating member of theengagement and disengagement device; and a seat belt having one endportion fixed to the reel, wherein the reel can wind the seat belt whenrotating in the first direction of rotation, and can unwind the seatbelt when rotating in the second direction of rotation opposite to thefirst direction of rotation.